Better acting, usually. Also, many of those older movies were made for the sake of making great movies, not just purely for profit like they are now. That's why a lot of the best movies these days are foreign - Hollywood will just make any crap that they think will sell and never take a chance on something original.
Blade Runner Reservoir Dogs Cinema Paradiso, have not watched Hugo yet The Dark Knight Brazil There Will Be Blood Harold and Maude Tree Of Life BQ2- Yeah, I was working on a project that day and I really needed it BQ3- Haven't watched it
I think older movies rely more on plot, acting and storytelling. That isn't to say that movies today aren't well made, well acted and tell good stories, some are, but older films didn't have anything technical or fancy to fall back on. Even soundtracks in older movies are far simpler and not as distracting. It depends on the film of course, but in general I think older films were held to a higher standard than today's. They took longer to film, yet weren't as expensive. Fewer movies came out in theaters yet the aura surrounding the business was more in awe and more respectful than it is today. I think money has a lot to do with it, when the only thing someone is thinking about is profit, quality inevitably becomes a victim of circumstance.